The kinetics and biochemistry of the recovery from radiation-induced cycle delay are to be studied as a function of stage in the cell cycle in Chinese hamster cells utilizing the mitotic cell collection procedure to precisely analyze the kinetics of division delay, and the incorporation of 3HTdR and subsequent liquid scintillation counting and autoradiography (CPM/labeled cell) to analyze the perturbation of DNA replication (S delay). The following questions are being asked: 1. What is the nature of the two component repair process of radiation-induced division delay? Does the recovery from radiation-induced S delay exhibit the same rate kinetics as the recovery from division delay? 2. What is the effect of inhibition RNA or protein synthesis on the cycle delay repair processes? 3. What are the kinetics and the biochemical nature of the recovery from hyperthermia-induced cycle delay? How does the damage from radiation and the damage from hyperthermia interact at the level of impaired cycle progression? 4. What is the effect of gene dosage on the recovery from radiation induced and heat-induced cycle delay? This experimental system will provide an answer through the application of two dose fractionation to our strain of tetraploid Chinese hamster cells. With this information the role of cell cycle progression, parasynchronization, and repopulation between fractionated doses of irradiation will be more clearly defined. These parameters could be more fully utilized to enhance the effectiveness of radiation in human cancer therapy.